Fuse



Dec- 1, 1942- l.. SCHMIDT 2,303,661

FUSE

Filed Jan. 2v. 1941 r11/nm 111111,11 I

Olli/111111111 Patented Dec. 1, 1942 FUSE Lambert Schmidt, Leeds, N. Y., assignor to Jefferson Electric Company, Bellwood, Ill., a corporation of Illinois Application January `27, 1941, Serial No. 376,078

3 Claims.

This invention relates to fuses for electrical circuits, andfmore particularly to fuses adapted to withstand moderate overload for a safe interval of time, and quickly to interrupt the circuit without explosion upon excessive overload or an overload which exceeds a predetermined safe period.

For as much of the subject matter disclosed, but not claimed in my copending application, Serial No. 196,841, filed March 19, 1938, which has since become Letters Patent No. 2,234,480, which subject matter is also disclosed herein, priority of the identified earlier application is claimed.

In the development of fuses, inventors and manufacturers have constantly endeavored to increase the safety of the operation and use of the fuses, and have met with several principal faults in the priory fuse constructions. One fault is the possibility of dangerous explosions due to the gases given off by the burning of the fuse metal when it is subjected to excessive current. Another fault is that a continuation of the burning of the fuse metal takes place. Another fault is presented due to the lack of any indication showing Whether or not the fuse has opened the electrical circuit. Still another fault with many fuses is that they break the circuit almost instantaneously when only moderate overload occurs, which overload could be very safely carried by the fused circuit for a reasonable period.

It is an object of this invention to provide an improved electrical fuse which corrects these difficulties by electing rupture of the fuse `link without excessive burning and quick separation of the ends of the fuse link to thereby isolate the parted ends and prevent continued arcing and the consequent formation of gases. This object is accomplished by providing a spring urged element which subjects the fuse link to a stress such that the circuit through the link is disrupted With theaid of mechanical force before it is liquied or burned up.

Another object of this invention is to provide a .fuse structurewhich may be quickly and easily inspected to ascertain Whether or not the circuit through the fuse has been interrupted and to thereby obviate the necessity of resorting to trial of different fuses to determine operative condition. This object is accomplished by .providing 4an inspection aperture in the fuse and a movable element which changes position when the circuit is interrupted and which is clearly visible through the inspection aperture. 55

Another object of this invention is to provide, in a fuse structure, any element Which effectively cools the fuse metal and thereby provides delay in the accumulation of heat by the fuse element so that the element does not disintegrate or burn out due to a momentary overload. For instance, in fuses of certain sizes, a current overload of 135% of rated capacity, is safe and permissible for periods up to one hour, This object is accomplished by an arrangement of parts such that a portion of one side of the fuse element engages a body of insulating and heat absorbing material so that some of the heat produced by the current flow through the fuse element is effectively conducted away from the element.

Another object of this invention is to provide means for deadening or quickly interrupting the spark at the fusing point of the fuse link when it is ruptured. This object is accomplished by mechanically separating the ends of the ruptured link at the instant of rupture.

In one aspect of this invention, it consists of providing a cartridge type fuse in which the fuse link is quickly disrupted When the part intended to be fused is brought to a predetermined fusing temperature.

In another aspect, this invention contemplates the separation of the parts of the fuse link after that link has reached its fusing point and the maintenance of such separation of the parts at a distance from each other by an insulating barrier. An insulating barrier under a spring or similar force quickly separates the link and acts as a barrier between the broken ends thereof ,to prevent the ends from again coming in contact.

It is another object of this invention to provide a fuse of the cartridge type having any or all of the aforementioned qualities or advantages.

This invention, as shown in the illustrated embodiments, not only provides for a high degree of safety in electrical fuses of the cartridge type, but also provides fuse structures which are dependable and consistent in operation and which are explosion-proof.

Other objects and advantages of this invention will be apparent from the following description taken in connection With the accompanying drawing in which similar characters of reference indicate similar parts throughout the several views.

In -the drawing:

Figure V1 is a side elevation view of a cartridge fuse embodying one form of the present invention;

Figure on a line 2 is a sectional view taken substantially 2-2 of Figure l and looking in the direction of the arrows, which view shows the fuse link in its normal and operative position;

Figure 3 is a sectional view similar to that of Figure 2 but showing the positions of the parts of the fuse after the link has reached a fusing point and has been ruptured;

Figure 4 is a sectional View taken substantially on a line 4-4 of Figure 2 and looking in the direction of the arrows;

Figure 5 is a side sectional view similar to that of Figure 2, but illustrating a somewhat different or modified cartridge fuse structure embodying the present invention;

Figure 6 is a sectional view of the modified fuse structure illustrated in Figure 5 with the section taken substantially on a line 6-6 of Figure 5 and looking in the direction of the arrows;

Figure 7 is an enlarged fragmentary sectional view with the section taken substantially on a line 1-1 of Figure 5 and in the direction of the arrows; and

Figure 8 is a perspective view of a preferred type of lpart utilized in the fuse structure shown in Figure 5.

Having particular reference to Figures l to 4 inclusive, the illustrated cartridge type fuse has a tubular housing I9 which is preferably made of insulating material. When the insulating material of which the housing I is made is opaque, as for instance fiber, it is preferable that one or more inspection apertures suoli as I I and I2 shall be provided in the wall of the housing so that the operative condition of the fuse may be determined by inspection. Since the fuse structure herein disclosed is explosion-proof, the tubular housing I may be made of glass or transparent plastic material so that the internal structure and condition of the fuse may be easily observed without the necessity of inspection apertures. When the inspection apertures are provided in a housing of opaque material, it is preferable that they should be covered with a transparent material to provide a closure for the openings.

Metal caps I3 and I4 fit over the ends of the tubular housing to close the ends and provide terminals or connectors for the fuse. A space of predetermined volume is defined by the tubular housing and the caps.

The cap I3 has a projecting member I5 secured thereto, as by riveting at I or other suitable means. The projecting member I5 has a flange I1 thereon which provides a shoulder and has a stem IB which projects into the interior of the fuse housing. The stem I8 preferably has a flanged covering sleeve I9 which covers the stem and fits into the tubular housing IQ adjacent the flange I1.

A plunger or piston of insulating material is slidably mounted within the tubular housing I0. The insulating material of which this plunger is made is preferably such that it has heat absorbing qualities. Lava is an example of a satisfactory material for the plunger. A recess 22 is provided in one end of the plunger 2U and extends axially with respect to the axis of the tubular housing. ln the disclosed embodiment, and as a preferred structure, a compression spring 23 fits over the covering sleeve I9 on the stem I8 and extends into the recess 22 to bias the plunger away from the stem I8 and cap I3. Axially extending slots or recesses 24 and 25 are provided in opposite sides of the plunger or piston 2D and a hook-shaped notch 26 adjoins the slot or recess 24 near one end thereof.

One end of a fusible ribbon-like fuse element 21 is anchored by the projecting member` I5 between the flange I1 and cap I3, Normally the fuse element 21 extends along the slot or recess 25 and over the end of the plunger 2D and has the other end anchored by a hook-shaped portion 28 of a conductor 29 so that the fuse element holds the plunger 20 adjacent the cap I3 against the biasing force of the compressed spring 23, as shown in Fig. 2. The fuse element 21 preferably has a portion of reduced section at 39 near the middle of the end of the plunger.

The conductor 29 is secured and electrically connected to the cap I4, as by soldering at 32. A circuit is completed from the cap I4 through the conductor 29 and the fuse element 21 to the cap I3. When the fuse element is ruptured as a result of an excessive current flow therethrough, the spring 23 forces the plunger 20 away from the cap I3 to separate and provide a barrier between the ends of the ruptured link. The conductor 29 is preferably deformed so as to have an angularly disposed portion 33 which provides a stop for the plunger to stop it between the ends of the ruptured fuse link and adjacent the aperture II and I2.

Referred particularly to Figs. 5 to 8 inclusive, a tubular housing 35 is made of insulating material and in a manner similar to that described with respect to the tubular housing I0, except that due to the disposition and nature of the parts within the housing, an inspection aperture 36 is preferably disposed nearer one end of the housing when such inspection aperture is utilized. End caps 31 and 38 are fitted over the ends of the tubular housing 35 in a manner similar to that described with respect to the end caps I3 and I4 and are preferably rolled into or against the tubular housing at the edges, as indicated at 39 and 40 to secure the end caps in position.

Parts comprising a base element 42 of insulating material, a plunger or piston 43 of insulating material similar to that defined with respect to the plunger 2U, a compression spring 44, a fuse element 45 and fuse element anchoring members 46 and 41 are preferably assembled as a separate sub-assembly before being mounted and secured within the tubular housing 35. The base element 42 preferably has dovetail notches 48 and 49 on opposite sides thereof and an integral projection 50 projecting from one of the surfaces thereof. The plunger 43 has a recess 52 therein and the compression spring 44 fits over the projection 5U and into the recess 44. The fuse element 45 has integral protuberances 53 and 54 which fit into apertures 55 and 56 in the anchoring members 46 and 41. The anchoring members 46 and 41 each have, as indicated in Fig. 8, side ears such as 51 and 58 which fit into and conform to the dovetail notches, and also have integral projecting lugs such as 59 and 60 which are adapted to engage the surface of the base element 42 when the anchoring members are in position in the notches. It is also preferable to provide soldering lugs 62 and 63 on the anchoring members to which conductors 64 and 65 respectively are secured by soldering. After assembly of the described sub-assembly, it is secured within the tubular housing 35 by fastening means such as screws or pins 6E and 61.

The conductors 64 and 65 are secured and electrically connected to the caps 31 and 38 by soldering-as-atlG-and 69,'to provide an electrical circuit rfromithe. cap 3'1- through the conductor 64, fuse element' 45 and conductor 5 to thecap 38. Thestop Amemberllllhas `a notch T2 Von oneside 'thereofthrou'gh which the` conductor 65` extends.

A stop member 10, which preferably comprises a ringof-insulatingmaterial, is fitted into the end of the tubular housing 35 opposite the base element 42 and near the inspection aperture 36 to stop the longitudinal movement of the plunger 43 in a position such as that indicated by the dot and dash lines at 43a when the fuse element is ruptured. This stops the plunger between the ends of the ruptured fuse element and adjacent the inspection aperture 36. The plunger 43 preferably has two oppositely disposed surfaces which conform to and slidably fit into the tubular housing 35, and also has intermediate flattened surfaces 'I3 and 14 which are spaced from the inner surface of the tubular housing. The fuse element 45 extends across the end of the plunger 43 and along the flattened surfaces 'I3 and '14. As in the previously described structure, the sectional area of the fuse element is preferably reduced at l adjacent the middle of the end surface of the plunger 43.

In the fuses disclosed, the engagement between the fuse element and the plunger enables the plunger to absorb heat from the fuse element during the operation of the fuse so that the fuse element does not immediately deteriorate and rupture upon the occurrence of a momentary moderate overload. In fact, the strength of the compression spring, the material and size of the plunger and the characteristics of the fuse element are preferably so chosen that the fuse element will withstand a moderate overload for a reasonable period before breaking the circuit. For example, a load of 135% of rated capacity is safe and permissible for periods up to one hour. For constant performance of fuses of this type made in production, it is desirable that in addition to having uniform fuse elements, the size and characteristics of the plunger should be practically uniform and the Volume of the interiors of the fuses should be relatively similar.

The volume of air within the interior of the fuse is somewhat effective upon the time-lag before rupture of the element on a moderate overload, as are the volume and material of the plunger, because the confined air and the plunger are heated by the fuse element during the overload period. The time required for a temperature rise to become sufcient to soften or disintegrate the fuse element on a moderate overload is consequently controlled by these factors.

It is important to note that in the disclosed structures the fuse element preferably has a portion of reduced section at the end of the plunger. This effectively weakens the fuse element at that point and brings about a weakening of the fuse element at that section, or in effect a concentration of the heat at the portion of reduced section so that the fuse element will be broken at the end of the plunger and the plunger will pass between and separate the severed ends of the fuse element quickly to extinguish the arc. By stopping the plunger between the severed ends of the fuse element, the insulating barrier remains between those severed ends and prevents them from rfa-engaging.

It is also important to note that stress is continually applied to the vfuse element during the normal operation of the fuse and during the heating of the fuse element by the flow of electrical of fuse in flwhich' actual' currentltherethrough. f Asthe fuse element heats,

it softens ordeterioratesito an extent `that it is ruptured by the mechanical force` applied thereto through'- theA plunger by the`v compressed spring. Thiais somewhat in contrast to ythe usual form meltingror burning of theefuse elementi is necessary toits disintegraion and the breaking of the circuit. Breaking of the circuit with the aid of mechanical force, as accomplished in the fuses disclosed herein, minimizes the necessary burning or fusing of the fuse element and thereby minimizes the creation of gases which often cause explosions of the usual types of fuses. The fuse metal and size of the fuse element and the spring characteristics are chosen to provide the desired mechanical stress for separating the ends of the severed fuse link upon rupture thereof and also to provide the desired time-lag between' the commencement of a predetermined moderate overload and the braking of the circuit by the fuse element.

While the embodiments of the invention which are illustrated and described herein are preferred forms, many modifications may be made without departing from the spirit and scope of this invention, and it is therefore intended that the invention shall not be limited to the precise details set forth, but shall include all changes coming within the scope of the appended claims.

What is claimed is:

1. A cartridge type fuse comprising, in combination, a tubular body of insulating material metal end caps fitting over the ends of the tubular body to provide a closed fuse housing having predetermined volume and providing terminals for the fuse, a plunger of insulating material having a recess in one end thereof and slidable longitudinally within the tubular body, a compression spring having one end disposed within said recess and biasing the plunger longitudinally of the tubular body, means providing a stationary support for the other end of the spring, a strip of fusible material disposed over the end of the plunger and having protuberances at the ends s thereof, means engaging said protuberances to anchor the ends of compressed and the trically connecting the strip so that the spring is strip is stressed, means electhe ends of the strip to the upon rupture of the strip so that the plunger provides an insulating barrier between the ends of the ruptured strip.

2. In a fuse, the combination comprising a base element of insulating material having oppositely disposed dovetail notches in the sides thereof, a plunger of insulating material, spring means biasing the plunger away from the base element, a fuse link having integral protuberances near the ends thereof and disposed over the end of the plunger, lugs having side portions fitting into the dovetail notches and ears resting against one side of the base element, said lugs being disposed in the dovetail notches over the ends of the fuse link and having openings fitting over said protuberances to anchor the ends of the fuse link, said fuse link normally holding the plunger adjacent the base element against the biasingdorce of said spring means.

3. A cartridge type fuse comprising, in combination, a tubular housing of insulating material; a sub-assembly secured within the tubular housing and including a base element of insulating material having oppositely disposed dove tail notches in the sides thereof, a plunger of insulating material, spring means biasing the plunger away from the base element, a fuse link having integral protuberances near` the ends thereof and disposed over the end of the plunger, lugs having side portions fitting into the dovetail notches and ears resting against one side of the base element, said lugs being disposed in the dovetail notches over the ends of the fuse link, said fuse link normally holding the plunger adjacent the base element against the biasing force of said spring means; terminals secured to the fuse; and means electrically connecting the terminals to the ends of the fuse link.

LAMBERT SCHMIDT. 

